Modern medicine uses many diagnostic procedures where electrical signals are received from a mammalian patient's body. Nonlimiting examples of diagnostic procedures include electrocardiograph (ECG or EKG) diagnosis or monitoring of electrical wave patterns of a mammalian heart. The point of contact between medical equipment used in these procedures and the skin of the patient is usually some sort of biomedical electrode. Such an electrode typically includes a conductor with a conductive medium adhered to or otherwise contacting skin of a patient.
For each diagnostic procedure, at least one biomedical electrode having an ionically-conductive medium containing an electrolyte is adhered to or otherwise contacts skin at a location of interest and also electrically connected to electrically diagnostic equipment. A component of the biomedical electrode is the electrical conductor in electrical communication with the ionically-conductive medium and the electrically diagnostic equipment.
Electrical conductors require excellent electrical conductivity and minimal electrical resistance for biomedical electrodes, especially when faint electrical signals are received from the patient. For this reason, metals or carbon are principally used. Among metals, silver is preferred because of its optimal conductivity. Biomedical electrodes which monitor a patient's conditions must be able to withstand the polarizing effects of a defibrillation procedure for a heart. So, a polarizable biomedical electrode with carbon or graphite conductor as shown in Japanese unexamined patent publication No. 4-236940 is not suitable for the application of the defibrillation. For this reason, silver chloride is preferably used with a silver conductor to create a depolarizing electrical conductor in biomedical electrodes.
The typical electrical conductor containing silver/silver chloride(Ag/AgCl) includes the Ag/AgCl eyelet which is electroplated with silver and converted the surface of silver (Ag) layer to silver chloride (AgCl). Recently, disposable, thin and flexible electrodes with thin and flexible conductor sheet which is formed by coating with Ag/AgCl ink on the thin and flexible plastic film was developed as shown in U.S. Pat. No. 5,078,138(Strand et al.). There is a principal difficulty with a biomedical electrode containing Ag/AgCl conductor. The cost of electrodes containing Ag/AgCl conductor has been greater than desired for a disposable electrode device.
In order to reduce the amount of Ag/AgCl used in biomedical electrodes, two kinds of solutions have been attempted. One was to use a conductor containing inexpensive graphite, carbon or other galvanically inactive materials in association with Ag/AgCl, such as those electrodes disclosed in U.S. Pat. No. 3,976,055 (Monter et al.). However, the electrode was still expensive due to the presence of Ag/AgCl particles that had to be located on the surface of conductor in order to keep good electrical performance.
Another attempt was to form Ag/AgCl layer on inexpensive graphite layer, carbon layer or other galvanically inactive material, such as that disclosed in U.S. Pat. No. 4,852,571 (Gadsby et al.) or Japanese unexamined patent publication No. 5-95922 (Sakagawa). However, the manufacturing cost was greater for these dual layer conductors than the cost for a single layered conductor, because the dual layered conductor had to be coated with two kinds of materials. Further, a significant amount of Ag/AgCl was used in the conductor to achieve good electrical performance.